ECE1390 RF L4 - Transceiver Architectures.pdf

RX Architectures

Zero/Low IF Architecture

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  • RF signal gets down-converted to around DC
  • image rejected in digital domain

FSK Signals

  • simple limiter for ADC can be used if wave crosses zero once per symbol
  • only possible with low FSK modulation index and low IF

Ultra Low Power

  • Zero IF is better for image rejection compared to Low IF, but it requires more power.
  • Zero IF is more sensitive to flicker-noise/DC-offsets, harder to demodulate
  • LO consumes most power in receiver

Low IF Architecture with Complex Filter

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  • Complex Filters have asymmetric frequency response around zero
  • limits possible image rejection but 90 shift is not required
  • can be shifted symmetrically around DC with sign inversion, allows two IF channel (symmetrical around LO) selection

Quadrature on RF Path

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  • reduces the power consumption from local oscillator by half
  • increase losses on RF path and reduces quadrature accuracy

Sliding IF Architecture

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  • image can be rejected by SAW filter with a low frequency for first mixer
  • much lower LO power consumption and front-end complexity
  • ,
  • larger tuning range required compared to a low-IF scheme
  • image rejection is limited by the pass-band filter

Injection Locking Architecture

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  • RF input locks VCO, VCO must be LC
  • relies on amplitude variation of VCO when locked outside peak resonance
  • very low complexity
  • only useful for phase modulated signals and sensitive to close blockers

Subsampling Architecture

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  • reduces power consumption and complexity of LO
  • requires high-q pass band filter

Mixer First Architecture

  • no LNA required but TIA will consume more power
  • LO leakage is a concern when LNA and mixer are not isolated
  • quadrature generation relies on LO

TX Architectures

Direct-Up Architecture

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  • similar to Zero-IF RX

Polar Architecture

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  • avoids up-conversion mixer by using decomposed mag. and phase signal

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Open Loop Modulation

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  • PLL suppresses modulating signal and VCO phase-noise within
  • open the loop during transmission to limit power consumption from settling time

Two Point Modulation

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  • relaxes trade off between and modulating signal
  • requires calibration scheme

Direct Modulation

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  • simple PLL can be used with constant envelop signal

Linearization with Non-Linear Component (LINC)

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  • more efficient than linear amplifiers but require constant envelop signals